1. Field of the Invention
This invention relates to improved optical systems and fibers, and in particular to optical systems and fibers that are specially adapted for long-haul undersea optical transmission.
2. Background Art
There is an ongoing demand for undersea long-haul optical transmission spans with increased lengths and data transmission rates. In order to achieve these objectives, the optical properties of the transmission components must be configured to achieve acceptably low levels of attenuation (i.e., transmission loss) and splice loss, while also maintaining acceptably low levels of dispersion and non-linearities.
Typical undersea long-haul transmission spans therefore commonly employ lengths of a negative-dispersion non-zero dispersion fiber (NZDF) combined with lengths of a dispersion compensating fiber (DCF) to control the amount of accumulated dispersion over the transmission span. An undersea optical fiber transmission span according to the prior art may include other components for providing amplification, as well as dispersion slope management.
The design of these transmission spans is complex because a number of conflicting considerations must be taken into account. For example, certain designs may call for the use of specialty fibers that provide management of both accumulated dispersion and dispersion slope. However, such fibers typically have relatively small effective areas, with increased attenuation and splice loss. In addition, such fibers are also typically difficult to design and costly to manufacture.
It should further be noted that because of the highly competitive nature of the fiber optics industry, there is an ongoing effort to reduce costs. An undersea transmission system can have a length of 10,000 km or more. Thus, even an apparently modest reduction in manufacturing and installation expenses can have a significant impact on the overall cost of a long-haul system.